A conventional method of determining crystallographic properties such as an orientation of a lattice structure at plural locations of a sample comprises generating an electron beam having electrons of a given mean kinetic energy and a given kinetic energy range, directing the electron beam to the plural locations of the sample, detecting an electron diffraction pattern for each of the locations, analyzing the electron diffraction patterns comprising Kikuchi bands, and determining the crystallographic properties for the plural locations based on the analyzed electron diffraction patterns. The kinetic energy range may be sufficiently small so that electron diffraction patterns may be obtained. Accordingly, for each of the locations, an electron diffraction pattern is detected and analyzed and the crystallographic properties are determined based on the analyzed diffraction pattern.
When detecting the diffraction pattern in transmission, i.e. on a side of the sample opposite to a side onto which the electron beam is incident, the sample must be sufficiently thin. Otherwise, if the sample is not sufficiently thin, the diffraction pattern may show insufficient contrast and, accordingly, may not yield proper results.
Furthermore, if the sample is not sufficiently thin, the diffraction pattern may comprise Kikuchi bands originating from multiple different sections of the sample disposed along the direction of the electron beam resulting in a superposition of plural individual diffraction patterns of each section. In this case, the diffraction pattern may indicate plural different crystallographic properties.
Another problem arises even for sufficiently thin samples, if the sample is of inhomogeneous thickness in a region, the crystallographic properties of which are to be determined. The kinetic energy of the electrons of the electron beam incident onto the region of inhomogeneous thickness may be selected as to provide diffraction patterns of good quality for a first thickness of the sample within the region. However, the diffraction pattern originating from locations where the sample has a thickness different from the first thickness are usually blurred and suffer from too little scattering power or too large absorption of the sample. Accordingly, a problem of conventional methods is that the crystallographic properties of a sample of inhomogeneous thickness cannot be properly determined.